Ondo (音頭 Ondō?) is a type of Japanese folk music genre.
The literal translation of "ondo" is "sound head." Kanji, or the Chinese characters used in the Japanese language, often have literal and abstract meanings, here the kanji for "sound" (音-on) having a more abstract meaning of "melody" or "music," and the kanji for "head," (頭) having a more abstract meaning of "beat," "base pattern." Hence "ondo" probably refers to a kind of "sound" or "beat pattern."
There are other names used to describe older Japanese genres of music. For example, "fushi" or "bushi" (節), with its literal meaning of "node," "knuckle," or "joint," refers to the nodes found in bamboo, usually found at a steady sequence. Thus "fushi" can also have the abstract idea of "sequence" to refer to notes and beats in a sequence, i.e., a melody.
An "ondo," however, usually refers to a kind of song with a distinct swung 2/2 rhythm. This "swing" can be referred to as "ukare" in Japanese. "Ondo" is a term used in older Japanese genres, but it is still used today when referring to songs written in this swinging style. Sometimes the rhythm is NOT swung and it is played straight through. This is called "kizami".
Not every old Japanese melody with a swung rhythm is called an "ondo," as sometimes the term "fushi" or "bushi" is used to refer to a tune with a swung 2/2 rhythm, both of these having more or less the same meaning of "tune" or "melody." The folk song Goshu Ondo, for example, does not follow this rule, as the rhythm is NOT played in a swung fashion. The folk song Tankō Bushi has a swung 2/2 rhythm, even though it has "bushi" in its name.
In Japanese folk music, "fushi" and "ondo" follow the name of the song. For example, Tokyo Ondo, Mamurogawa Ondo, and Hanagasa Ondo all have "ondo" in their names. Kushimoto fushi, Burabura fushi, and Soran fushi all have a rendering of "fushi" in their names.